Separated scaling from the sandbox.

Makes it easy to write your own scaling functions if desired; there
is nothing to replace/work around.
Scale class makes it easy to convert things and is a good place to
start when considering the relationship between your screen space
graphics and physics space bodies. I recommend using it, but you're
not bound to it like you were when it lived inside of Sandbox.
Updated drawing sample to work with new scaling location.
Updated Sandbox sample to use new scale object.